1. Technical Field
This invention relates to electrostatographic reproduction apparatus, and more particularly, to a sheet holding tray in such apparatus having accurately positionable adjustable sheet size guides.
2. Background Art
In modern reproduction apparatus, such as electrostatographic copiers or printers, for example, a latent image of information to be reproduced or copied, is formed on a uniformly charged dielectric member by altering the charge thereon in an image-wise pattern. The latent image charge pattern is then developed with toner or pigmented marking particles. Thereafter, the developed image is transferred to a selected copy sheet of a particular size and fixed to such sheet by applying heat and/or pressure thereby forming the desired reproduction or copy.
In order to improve the productivity of such reproduction apparatus, it is known to provide therein logic and control means, copy sheet feeding and copy handling means, and sheet paths all capable of enabling the apparatus to reproduce or copy information on both sides of a copy sheet. Reproduction apparatus enabled as such are said to be capable of performing duplex copying. Duplex copying may be accomplished in a single pass of a copy sheet through the reproduction cycle of a reproduction apparatus (single pass duplexing), or in two passes of the copy sheet through the reproduction cycle (double pass duplexing). For single pass duplexing, developed images of appropriate information are transferred respectively to each side of a copy sheet and then fixed simultaneously to such sheet. On the other hand, for double pass duplexing, a receiver sheet feed path is provided and includes an intermediate or duplex sheet holding tray in which receiver sheets, after each receiving and having a developed first image on a first, fixed side thereof, are held and then refed seriatim at a subsequent time from the duplex or intermediate tray for each receiving a second image on the second and opposite side thereof. The developed second images on the second sides are thereafter also fixed by applying heat and/or pressure.
While double pass duplex copying is typically somewhat slower in overall reproduction productivity than single pass duplex copying, double pass duplex copying does simplify handling of copy sheets during transport to the fixing device. This is due to the fact that only one side of each copy sheet being fed to the fixing device bears an unfixed toner image. However, the use of an intermediate or duplex sheet holding tray in reproduction apparatus as above for duplex copying undesirably exposes the reproduction apparatus to the possibility of several operational problems. For example, after a first image is fixed on the first side of a copy sheet, such sheet must be held in a duplex tray and refed such that the second image is properly registered on the second side of such sheet. As disclosed for example in U.S. Pat. No. 4,949,134, it is known to provide sheet edge guides in a sheet holding duplex or intermediate tray for aligning sheets held temporarily within such tray in order to improve subsequent refeeding and registration of the sheet.
Because reproduction apparatus use different size sheets, this, however, means that such sheet edge guides of the duplex tray must be positioned, moved and repositioned with substantial precision each time a different size copy sheet is to be used in the reproduction apparatus. Imprecise positioning of these guides, of course, results in poor sheet alignment within the tray and subsequently in poor image-to-sheet registration at image transfer. Over-travel movement, (i.e., movement that requires the sheet edge guides to always return to a home position which is marked by a limit switch) is additionally time consuming and slow. In particular, recovery times in such a home-position controlled system is very slow following an accidental power shutdown of the power supply of such a system because it has to be started all over to work.